The present invention relates to an image forming method used for the image formation of the electronic photographing method, an image forming apparatus and an organic photoreceptor, and in more detail, to an image forming method used for the image formation of the electronic photographing system used in a field of a copier or a printer, an image forming apparatus and an organic photoreceptor (hereinafter, simply called photoreceptor).
The main subject of a photoreceptor is transferred from an inorganic photoreceptor such as Se, arsenic, arsenic/Se alloy, CdS, ZnO, to an organic photoreceptor which has advantages in the environmental pollution, or easiness of manufacturing, and the organic photoreceptors using various materials are developed.
Recently, the function separation type photoreceptor in which functions for generating the electronic charge and for charge transportation are made in charge to different materials, becomes the main stream, for example, a laminated type photoreceptor in which the charge generating layer, charge transporting layer are laminated through the intermediate layer on the conductive supporting body, is widely used (Patent Document 1).
Further, when looks at the electronic photographic process, in the latent image formation system, it is largely separated into an analog image formation using the halogen lamp as a light source and a digital system image formation using LED or laser as a light source. Recently, as a printer for hard-copy of the personal computer, further, also in the normal copier, from the easiness of the image processing or the easiness of the development to the composite machine, the digital system latent image formation system is rapidly becoming the main stream.
Further, in the digital system image formation method, the opportunity for making the print image of the original is increased, and the requirement for the high quality image is increased. For the high quality image-making of the electronic photographing image, a technology by which the minute latent image formation is conducted by using the light source for exposure whose spot diameter is small, on the organic photoreceptor, and the minute dot image is formed, is developed. For example, by using the light source whose spot diameter is less than 4000 μm2, a method by which the high accurate latent image is formed on the organic photoreceptor is well known (Patent Document 2). Even when the high density dot exposure is conducted by such a small diameter spot, the organic photoreceptor by which the high density and uniform latent image can be formed by the dot exposure, and the structure of the developing mode by which the latent image can be reproduced as a toner image, are not yet attained sufficiently. Further, in a dot image, there are problems that a transverse line image becomes thin (a phenomenon in which a one dot line image formed in a direction perpendicular to a paper conveying direction becomes thin in comparison with one dot line image formed in the paper conveying direction), and a trailing edge becomes white omission (a phenomenon in which the image density of a trailing edge portion of a halftone picture image in the paper conveying direction is lowered than the leading edge portion or the trailing edge portion is not developed).
That is, as the developing method of the latent image on the organic photoreceptor, a developing mode by which the developing sleeve oppositely provided to the organic photoreceptor is advanced in parallel with the advancing direction of the organic photoreceptor in the developing area (hereinafter, parallel developing mode), and a developing mode by which the developing sleeve is advanced in the counter direction (hereinafter, counter developing mode) are well known, however, for both, when the high density dot image is formed, the problems can not be solved sufficiently.
In the parallel developing mode by which the developing sleeve oppositely provided to the organic photoreceptor is advanced in parallel with the advancing direction of the organic photoreceptor, the developing property of the periphery of the high density image is deteriorated, and is easily brought to the insufficient density, and in the photographic image whose contrast is high, the image quality is easily deteriorated.
On the one hand, in the counter developing mode by which the developing sleeve is advanced in the counter direction, the developing property is high, and the high density dot image can be formed, however, the fog is often generated, and the insufficient density is easily generated in the leading edge part.
Further, recently, a fine unevenness trouble so called a worm-like unevenness becomes a problem. Although the cause of this worm-like unevenness has not clarified sufficiently, it may be considered that when a relative velocity between a photoreceptor and a developing sleeve becomes faster and a triboelectric charging between a magnetic brush of a developer and a photoreceptor becomes stronger, the worm-like unevenness may occur. For this reason, in comparison with the parallel developing mode, the worm-like unevenness tends to occur in the counter developing mode. Further, the worm-like unevenness has a relative relationship with a frequency of the developing bias such that if the frequency becomes higher, the worm-like unevenness becomes fewer. However, when the frequency becomes higher, there is a tendency that the sharpness of an image becomes lowered. That is, it may be difficult to satisfy both of the reduction of the worm-like unevenness and the sharpness of an image.
The phenomena as described above, are not solved enough simply by only the improvement of the developer, but it is found that also by the characteristic of the organic photoreceptor, these phenomena are deteriorated or improved. That is, it is presumed that these phenomena relate to the contrast of the electro-static latent image formed on the organic photoreceptor, or also to the generation of the inverse charge toner by the rubbing of the organic photoreceptor and the developer.
In the counter development method, due to the contact friction between the photoreceptor and the toner, it is easy for oppositely charged toner to be generated, and as a result, fog or toner splashing can occur, or it is easy for edge section density reductions to occur, and it is not possible to reproduce high resolution electrostatic images as toner images. In other words, although reducing the quantity of oppositely charged toner generated due to the contact friction between the photoreceptor and the toner is considered very important in preventing the occurrence of these fog and edge section density reductions, so far not much research results have been disclosed regarding the surface physics of organic photoreceptors suitable for the counter development method.
[Patent Document 1] Tokkai No. 2003-316203
[Patent Document 2] Tokkai No. 2001-125435